High-modulus, high-tenacity, lowshrinkage polyamide yarn



Feb. 7, 1967 G. PITZL 3,303,169

HIGH-MODULUS, HIGH-TENACITY, LOW-SHRINKAGE POLYAMIDE YARN Filed Jan. 18, 1962 2 Sheets-Sheet l 3* P F l G. l 3

YARN PATH G. PITZL Feb. 7, 1967 HIGHMODULUS, HIGH-TENACITY, LOW-SHRINKAGE POLYAMIDE YARN Filed Jan. 18, 1962 2 Sheets-Sheet 2 EEG United States Patent Ofiice Bfifidifi Patented Feb. 7, 1967 3,303,169 HIGH-MOEULUS, HiGH-TENACITY, LOW- SHRENKAGE POLYAMIDE YARN Gilbert Pitzl, Chattanooga, Tenn., assignor to E. I. du Pont tie Nernours and Company, Wilmington, DeL, a corporation of Delaware Filed Jan. 18, 1962, Ser. No. 167,083 2 Claims. (Cl. 26078) This invention relates generally to the production of filamentary structures from synthetic linear polymers and more particularly to the processes by which polyamide filaments are drawn and oriented.

It is Well known that synthetic linear polyamide fila ments are usually drawn to increased length in order to produce an oriented structure having high tensile strength. When nylon was first introduced, this step was accompiished merely by tensioning filamentary yarn between feed and draw rolls operated at differential speeds. Although product quality was acceptabie, various difficulties such as differential dyeabiiity were encountered as a result of nonuniform tensile properties and variable orientation along the length of the drawn yarn. Subsequently, the use ofa snubbing pin in the draw zone and localization of the draw point on the surface of the pin were disclosed by Babcock in U.S. Patent No. 2,289,- 232. With this modification, yarn properties and uniformity are improved substantially but additional process considerations such as the application of finish to the yarn for the purpose of reducing friction are involved. To avoid variations in yarn properties, the amount, distribution and composition of the finish must be con trolled carefully. For a given set of process conditions, there is an upper limiton the speed with which yarn can be drawn in order to insure that adequate time is availabie for the uniform application of finish to each filament of a bundle. Similarly, where a heated pin is employed, there is a limit imposed on drawing speed by the minimum contact time required to heat the running yarn sufiiciently.

An additional problem which has been encountered in pin-drawing nylon yarn is that the drawn yarn undergoes a gradual length-wise retraction with time. These effects are accelerated by heat and moisture. For example, representative nylon yarns have a boil-off shrinkage of or more. Where that degree of shrinkage is excessive, a separate shrinking step priorto utilization of the yarn is required. In addition to the extra processing and handling involved in such preshrinking procedures, the yarn usually suffers a reduction in initial modulus due to a diminution of yarn orientation and is therefore more sensitive to tension variations encountered in subsequent processing stages.

The most important object of the present invention is to provide a single-stage, high-speed drawing process wherein high-modulus, high-tenacity, low-shrinkage polyamide yarn is obtained.

A further important object is the provision of process improvements which facilitate the continuous, high-speed production of yarn having especially uniform properties.

Another of my objects is to provide a high-speed process in which yarn may be drawn at a substantially constant low tension.

A corollary object of the present invention is the production, under certain process conditions, of a lowshrinkage, low-retraction"polyamide yarn having higher initial modulus and tenacity values than are obtainable under known process conditions.

These and other objectives are accomplished in a single-stage drawing process which includes the steps of advancing a filamentary structure over feed and draw rolls and substantially instantaneously heating the filaments in the draw zone to a temperature of at least C. as they pass'through an enclosure. In the enclosure, a heated, single-phase gaseous fluid is jetted 0n the filaments in intersecting relationship therewith, thereby reducing the drawing tension substantially and localizing a significant fraction of the draw in the enclosure.

As noted, the desired combination of properties is at tained only when a yarn temperature of at least 115 C. and preferably C. or more is reached. With a substantially instantaneous increase in filament temperature to about C., much more stable operation and improved product uniformity are achieved. The maximum operabie filament temperature corresponds to the fiber stick temperature which is generally about 20-35 C. below the polymer melting point. When this temperature is reached, it is believed that individual filaments break and stick to the body of the jet enclosure thereby fouling the yarn passages and rapidly breaking down the thread line. Broken filaments observed under these conditions show evidence of fusing.

Where reference is made herein to a substantially instantaneous increase in filament temperature, the relationship between fluid conditions and yarn speed is such that the yarn is raised to the desired temperature in less than ten milliseconds, preferably in less than about one millisecond. Under these circumstances, fluid temperatures above the polyamidemelting point are usually required but have no adverse effect on the yarn because of the high rate of speed at which it travels through the fluid jet.

Although a substantially instantaneous increase in filament temperature within the jet enclosure is an essential feature of the present process, it is apparent that such temperature measurements oftentimes can only be made with great difficulty.- Furthermore, in the lower range of operable filament temperatures, small variations can have a large effect on the degree of fiber orientation and, for that reason, the close control of process variables is important. In this respect, it-has been found that the reduction in tension resulting from the transfer of heat to the filamentary structures is an accurate reflection of the yarn temperature in the jet enclosure. Since the reduction in tension can be measured readily, it is also useful as a control parameter and has been reported herein as a process characterization. When the temperature and pressure conditions are sufiiciently intense to raise the yarn to a temperature of about 115 C., there is a corresponding reduction in tension in the draw zone to about 75% of the tension observed when no heating fluid is supplied. Much greater improvements are obtained when the drawing tension is reduced to the 65% level and below.

In addition to yarn temperature in the jet and tension level in the draw zone, the extent to which the yarn is aeoanes drawn is another-process variable on which the degree of orientation is dependent. However, since as-spun yarn is partially oriented, reference to the draw ratio alone does not give an accurate or reliable indication of the total orientation observed in the drawn yarn. Where the phrase total draw'ratio X is used herein, the various types of orientation introduced into the yarn have been considered. Thus, the factor X includes, the conventional machine draw ratio X which is the ratio of feed .and draw roll surface speeds if no slippage occurs. Since the yarn entering the drawing stage may be under slight tension, an added predrawing stretch ratio X may have been imposed; usually this orientation factor is insignificant and-can be ignor'ed. The as -spun yarn also has a degree of orientation, produced the spinning process and measured by filament birefringence, which can be expressed as a draw ratio X,,. With this information available, a reasonably accurate indication of the degree of orientation can be obtained by corriputingthe total draw ratio X which is the product of the machine draw ratio X and the as-spun orientation factor X Additional objectives, advantages and characterizations of the present invention will become apparent in'the following specification and examples wherein reference is made to the accompanying drawings in which: 7

FIGURE 1 is a'schematic illustration of an apparatus arrangement useful in. the practice of the present invention; I f

FIG. 2 is an enlarged, longitudinal; sectional view of the single orifice jet shown-schematically in FIG. 1; FIG. 3 is a schematic illustration of an apparatus arrangement difiering slightly from that shown in FIG. '1; FIG. 4 is a longitudinal, sectional view of a two orifice jet suitable for use as a replacement in the arrangements of FIGS. land 3;

FIG. 5 is a perspective view, partially sectioned, of another jet embodiment; and y it 7 FIG. dis a schematic illustration of an apparatus arrangernent which has been included for purposes of comparison.

In the process arrangement of .FIG. 1 (Example I),

undrawn polyarnidefilamentary yarn It is unwound from a package 12, moistened in its travel over finish'roll 14, passed between gui-depins 16 and tensioned between driven feed roll 18 anddraw roll. 26. In order that the filamentary structure will be drawn to several times its extruded length, rolls 18, 20 are operated at differential surface speeds, i.e., roll 20 has a.-peripheral speed considerablyhigher than that of roll 18. From roll 20, the drawn filamentary structure passes between pins '22 to a suitable windup 24.

In the draw zone between rolls 18," 29, a jet device 26 of the type-shown in FIG. 2 is positioned. Device 26 is provided with a longitudinal passage orenclosure 27 through which the tensioned yarn travels. Intermediate its ends, passage 27' communicates with theorifice of a jet conduit 28, which is disposed at an angle of about 30 with the axis of pass'age2'7. Device 26 is adapted for connection at 29.to a suitable high pressure fitting which functions to deliver a controlled supply of a single-phase heated gaseous fluid toconduit 28 for discharge into passage 27 in intersecting relationship with yarn passing therethrough in the direction indicated.

The process arrangement of FIG. 3 (Examples II, V) is similar to that shown'in FIG. 1 except that yarn 10'- is spun from a spinneret 12' and a tandem arrangement of two jet devices 26 is provided in the draw zone between rolls 18', 2t). V

In other process arrangements (Examples III,'IV' and VII-IX), the jet devices of FIGS. 4 and 5 are substituted for the device 26 of FIG..1 or for the devices 26' of FIG. 3. The device 4!} of FIG. 4 is similar to that shown in FIG. 2, except for the provision of two angularly disposed jet conduits 41, 42 discharging into the longitudinal passage 43 at an angle of 45. The jet device 50 of FIG. 5 has an initial passage 51 through which yarn travels to expansion chamber 52, passage 53 and tail pipe 54. In chamber 52, heated fluid from four symmetrically disposed jet conduits 55 is jetted onto the yarnin intersecting relationship therewith. I

The apparatus arrangement of FIG. 6 includes a plurality of pins 61 which support yarn 62 in the draw zone as heated fluid is discharged thereon from a plurality of jet conduits 63, each in communication with a manifold 64. This arrangement has been disclosed herein for purposes of comparison (Example VI) with operable embodiments wherein the yarn isin a passage or enclosure when exposed to the fluid jet. In this respect, it should be noted that the embodiments of FIGS. 4 and 5 have a pas sage or enclosure equivalent to that shown at 27 in FIG. 2, i.e., a passage which is.complete'ly enclosed except for the yarn inlet and outlet and the jetorifioe(s). Other constructions are feasible. For example, a device comprised of a pair of opposed flat plates between which the yarn travels as fluid is jetted thereon from an orifice in one of the plates is operable under certain conditions. The principal requirement is that the heated fluid must impinge on the yarn in an at least partially restricted zone. Fluid expansion in that zone of contact or impingement contributes to a separation of the yarn bundle and to the substantially instantaneous increase in filament temperature which is essential to the instant process. When these con ditions are achieved heat transfer from the gas tov the yarn is optimum, due at least in part to separation of the filaments in the yarn bundle during such treatment (Example III). The separation of the filaments also helps to avoid fusing athigh gas tem'peraturesQ Any gas reasonably inert to the yarn may be employed as the jet medium, hot air or superheated steam being preferred in.,most'applications. Other possibilities include nitrogen, carbon dioxide and mixtures thereof. Saturated steam is believedf toadv'ersely aflect the yarn modulus at temperatures required to obtain. minimum yarn shrinkage. In addition, the presence of condensate on the drawn yarn is thought to contribute .to product nonuniformity V v The temperature and pressure of the heated, singlephase gaseous fluid must be carefully controlled to maintain a product with uniform properties. At constant pressure, the temperature of the fluid determines the amount of tensionin the yarn during drawing as well as theshrinkage and retraction of the product. Any increase in fluid temperature at constant pressure results in a substantial decrease in all three values, the upper limitusually being set by temperatures at which filaments fuse or break in a given jet. Conversely, at constant temperature, an increase in fluid pressure not-only re stilts in a decrease in the yarn tension duringdrawing but also leads to a further reduction in the residual shrinkage and retraction of the drawn yarn. The temperature and pressure selected will also depend on yarn speed because of its relationship to the period of yarn exposure to the jet medium. A comparison (Table I, runs AF and AK) of the relative efficiency of superheated steam and hot airat the same pressure, using the same fluid jet, shows a distinct temperature advantage in favor of steam, as reflected by the level oftension during drawing and by the shrinkage and retraction of the product. I

In the examples which f01low,'the use of different combinations of the illustratedapparatus under various drawing conditions has been escribed. When polyamide filaments are drawnfinaccordance with the minirnum process regu'irements',jthe drawn yarn is characterized by' high modulus and'tenacity as well as by low shrinkage and retraction. It also has good'mcchanical quality and excellent property uniformity. Since snub b ing elements are not employed, the problems previously encountered with friction and finish uniformity are avoided.

Under the more severe process conditions reported in some of the examples, an unusual and hitherto unobtainable combination of properties is achieved in that the drawn yarn has a break elongation of at least 25%, an initial modulus of at least 38 grams/ denier and a boiloff shrinkage of not over 6.5%. X-ray analysis shows that the crystalline structure is highly oriented and has a large transverse area. The average X-ray orientation angle is preferably less than about 14, and the crystal cross sectional area is at least 1250 square Angstroms, preferably at least 1500 A measured prior to boil-off, relaxation or annealing treatments. This product is so stable that, even after boil-01f, its high modulus is largely retained and fabrics woven therefrom are characterized by an unusually high crease recovery, indicating superior wrinkle resistance and resilience.

The yarn samples employed in the exemplified tests and comparisons were obtained by stripping representative 130-150 cm. lengths from the extremities and from the longitudinal center of a package, throughout the entire package and yarn length.

Where retraction is reported, sample length was determined immediately after removal from the package by tying the ends of the sample together, hanging a weight equivalent to about 0.1 g.:p.d. in the loop and measuring loop length. After exposure for 24 hours at 75 F., 72% relative humidity, loop length was measured again and percent retraction was calculated.

For shrinkage values, yarn samples were taken from packages which had been conditioned for one day at 75 1 72% relative humidity. After determination of the initial length, a loop of conditioned yarn was submerged in boiling water for about minutes and then dried for about minutes under 0.1 g.p.d. tension. After measuring the length of the boiled-off loop, percent shrinkage was calculated.

The initial modulus, represented by the symbol M is defined as the ratio of change in stress to strain in the first reasonably linear portion of a stress-strain curve. The units employed herein make the initial modulus numerically equivalent to 100 times the force in grams per denier required to stretch the specimen the first 1%. In the examples, the modulus is obtained from yarn stressstrain curves recorded on an Instron Tensile Tester of the type which stretches the yarn at a constant rate of elongation. From the stress-strain curve, the slope of the initial straight line portion is determined graphically. Tenacity and break elongation are also read from the curve. All yarn tested was conditioned on the package for one day at 75 F., 72% relative humidity, prior to testing.

It is believed that the maximum benefits of the process of this invention are attained when the yarn is heated in the jet enclosure to a sufficiently high temperature to achieve a pseudo-hexagonal crystal structure, as determined by X-ray diffraction. The yarn is observed immediately after leaving the jet enclosure. Temperatures approximating the force-to-draw transition are usually required to produce this structure.

The force-to-draw transition temperature is the temperature at which a discontinuity is observed in the ratio of the logarithm of the tension required to draw an undrawn filament versus the reciprocal of the drawing temperature, as expressed in degrees on an absolute temperature scale. conveniently determined by forwarding filamentary yarn from the spinning wind-up package, at 2 /2 yards per minute, to and about a hot steel snubbing pin one inch in diameter and provided with a chrome-plated matte finish, the yarn being drawn 4.5X The drawing force is The force-to-draw transition temperature is.

specified, the discontinuity is readily identified and 7 evaluated.

. Crystal orientation and average lateral crystal dimenslons of the high modulus product of this invention are determined from the principal equatorial X-ray diffraction maxima. Polyamide diffraction patterns of this type are described by C. W. Bunn and E. V. Garner, Proc. Royal Soc., 1898A, 39 (1947), for example. Crystal orientation is actually calculated from the half widths of the equatorial reflections, determined from an azimuthal photometer trace, following the methods described by H. G. Ingersol in Journ. Appl. Phys, 17, 924 (1946 Crystal dimensions are estimated from the breadth of these diffraction spots, measured from equatorial photometer traces, according the the method of H. P. King and L. F. Alexander, X-Ray Diffraction Procedures, John Wiley and Sons,'Inc., New York, 1954; Ch. 9. Warrens correction for line broadening due to instrumental effects was used as a correction for Scherrers line broadening equation. Zinc voxide was the reference material. A value of 0.9 was employed for the shape factor K in Scherrers equation.

Where reference is made to the relative viscosity of polymer or yarn, it was determined as described in US.

Patent No. 2,3 85,890.

EXAMPLE I A 34 filament yarn was spun from molten polyhexamethylene 'adipamide having a relative viscosity of about Ito a spinning draw ratio X of 1.12. The total draw ratio X was therefore 4.48. After drawing, the yarn was wound at a tension of 10-15 gr-ams on a surface driven reciprocating traverse windup. The results obtained under various conditions of fluid temperature and pressure are reported (runs AC-AO) in Table I. In each of runs AC-AM, the heated fluid was at a pressure of 50 p.s.i.g. In runs AN and A0, the pressures were 25 and 65 p.s.i. g., respectively Runs AA and AB have been included for purposes of comparison. :In AA, an unheated snubbing pin of the type disclosed by Babcock was employed. In AB, the yarn was uncontrolled in-the draw zone, i.e., neither a pin nor a fluid jet was employed.

A reference to the drawing tensions and yarn properties reported in Table I shows that the advantages of .the present process begin to appear when fluid jet conditions are such that drawing tension is less than about 75% of that measured for the delocalized control in run AB, i.e., when the yarn temperature in the jet enclosure exceeds 115 C. In this respect, much better yarn properties are obtained with tensions less than about 65% of AB (filament temperatures above 119 C.) Under corresponding conditions of temperature and jet pressure, superheated steam (AK) is a more effective heat transfer fluid than hot air (AE). Equivalent yarn properties are obtained at a given tension level, regardless of the'identity of the jet gas.

The tabulation also shows that more than 25% of the draw must'occur (AF and AI) in the yarn passage of the jet device in order to achieve the desired combination of properties. Preferably (AG and AK), at least 50% of the draw is localized in that passage. In comparison with the accepted view that of the draw should be localized at a snubbing pin or its equivalent in order to obtain controlled drawing, it is interesting to note that good yarn properties are obtained at much lower percentages of localization in the present-process.

Table 1 Heat Transfer Draw Zone Yarn Properties Run Fluid p Fluid Yarn Tension, Tension, Percent Shrinkage, Refraction, Initial Temp, 0. Temp, O. g.p.d. Percent Draw in Percent Percent Modulus,

Control Enclosure g.p.d.

- Delocalized control.

EXAMPLE II In an apparatus arrangement of the type shown in FIG. 3, 34 filament yarn was spun from molten polyhexamethylene adi-pamide of 33.5 relative viscosity and drawn continuously to a total draw ratio of 4.5X. The yarn was drawn to a final denier of 70 and Wound at a speed of 2000 yards/min, at a tension of 7-10 grams. The two jet devices were spaced apart 1.5 inches along the yarn line. With this tandem arrangement, eifective heating of the yarn at the higher winding speed was achieved. Results obtained in a series of tests using superheated steam at different temperatures and pressures are reported in Table II.

1 Draw pin.

Example I and the tandem jet arrangement of Example II. The comparable control (AB from Table I) is included. A comparison of the results obtaind in runs BB-BK (Table II) andCA-CC provides additional support for the conclusion that an equivalent combination of properties can be achieved at a somewhat higher tension level with pre-pacleaged as against freshly spun yarn. A similar comparison with runs AJ-AL (Table I) shows that more effective heating is accomplished with the tandem jet arrangement and that incremental property improvements are obtained as the treatment conditions become more severe.

, .The test is thenrepeated using the jet embodiment of Table II Heat Transfer Draw Zone Yarn Properties Run Steam 7 Steam Temp;, C. Yarn Tension, Pressure, Temp, Tension, Percent Shrinkage, Retraction, Initial Mod- Crystallinity,

p.s.i.g. C. gpd. v Control Percent Percent ulus, g.p.d. Percent let #1 Jet #2 None 1.81 100.0 11.4 V 3. 0 30.8 35.1

The percent crystallinity was determined by the density method of Starkwe-ather and. Moynihan, Journal of Polymer Science, 22, 363 (1956). The determinations are based on an estimated density of 1.069 for amorphous nylon and a density of 1.220 for the crystalline regions. The density of yarn samples was determined by the method of Boyer, Spencer and Wiley, J. Poly. Sci, 1, 249

From the following table, it is apparent that the desirable combination of propertiesis not achieved, with freshly spun filaments, until drawing tensions are'reduced to a somewhat lower level than was required with the prepackaged yarn of Example I. It is also apparent that the yarn properties improve as the treatment becomes more severe. Although good results are achieved when tension is reduced to from 65-70% of the control run BA, 21 greater incremental improvement is observed when the'drawing tension is less than 60% of control. It is observed that the increased stability of the yarn (to retraction and shrinkage) is obtained with some increase in modulus, which is contrary to expectations.

EXAMPLE III 'Under the conditions shown in Table III, additional runs are made, using the same pre-paekaged yarn 'as in FIG. 5 in which superheated steam is jetted onto the yarn from four orifices disposed in planes at right angles. Yarn properties and test conditions for runs CE-CI are also reported in Table III. The results show that, with no increase in steam temperature, drawing conditions and yarn properties improve with each increase in steam pres sure. On the basis of these improvements, it is believed that an important factor in obtaining the advantages of the process of this invention is to provide gas to the jet conduit at a sufficient pressure so that the yarn bundle will be separated or splayed by vibration or otherwise into its individual filaments as a result of the impingement of the jet or jets thereon. As evidence to support this hypothesis, drawn 7O denier 34 filament yarn was attached to a. fixed support, passed through the jet of FIG. 5 and thence over. a pulley. A weight was attached to the yarn. The jet for this experiment was equipped with a glass tail pipe so that the yarn could be more easily observed. Room temperature air was passed through the jet. At an air pressure of 50 p.s.i. and at a dead load corresponding to the yarn tension in run CF, the yarn was observed to vibrate. It was observed that the air pressure must exceed 25 p.s.i. in order to maintain stable vibration. It was concluded that the air pressure in runs CF- .CI is in the range required to initiate and maintain stable vibration or splaying of the yarn bundle, at the drawing tension observed.

an apparatus arrangement similar to that shown in FIG. 3 except for the omission of one of the jet devices and Table III TANDEM JETS Heat Transfer Draw Zone Yarn Properties Run Steam Steam Temp, C. Yarn Tension,

Pressure, Temp., Tension, Percent Shrinkage, Reaction, Initial M od- Tenacity,

p.s.i.g. C. g.p.d. Control Percent Percent ulus, g.p.d. g.p.d.

Jet #1 Jet #2 FOUR ORIFICE JET Elongation, Percent EXAMPLE IV After replacing the illustrated jet device with that shown in FIG. 4, the apparatus arrangement of FIG. 1 was used enlargement of the yarn passage or enclosure in the remaining jet device. The heated fluid was superheated steam and the windup speed was 2000- yards/min., as in to draw pre-packaged 34 filament 66-nylon yarn (bi- 30 Example II. Denier uniformity of this yarn and of two refringence 0.005) of 36.5 relative viscosity at a machine draw ratio X of 4.0. The yarn was drawn to a final denier of about 70 and wound at a speed of 500 yards/ control yarns, as reported in the following table, was determined automatically by capacitance variation measurements using a Model C Uster Tester.

1 Piu-drawn control. 2 Delocnlized control. Percent. eoellicient of variation.

min. For purposes of comparison, deloc-alized control run EA and pin drawn run EB have been included in Table IV.

The increased crystallinity of the test yarns (runs EC- EG) compared with the pin-drawn control yarn (run EB) is readily apparent. The surprising tensile properties of the yarns of this invention are also demonstrated. For example, in the series of runs EC to EG, the yarn tenacity is seen to increase appreciably While the yarn elongation (break elongation) remains substantially constant.

Drawing tension for run PC is within the scope of the invention. The data in Table V show that the test yarn (run EC) is more uniform than the pin-drawn control (run PA) or the cold-drawn control (run FB). As in the preceding examples, the mechanical uniformity of the product and the operability level of the process are generally superior to those of the comparable operations involving a draw pin or other snubbing element.

EXAMPLE VI Pro-packaged 34 filament nylon yarn having a bire- T able IV Ileat Transfer Draw Zone Yam Properties Run Steam Pressure, Steam Yarn Tension, Tension, Per- Tenacity, Elongation, Crystallinity,

p.s.i.g. Temp, 0 Temp., C. g.p.d. cent Control g.p.d. Percent Percent EA 2. 86 100. 0 35. 5 EB 2. 50 87.5 5.1 27. 5 34. 1 E C 2. 07 72. 4 5. 8 27. 2 35. 1 ED 1. 86 65. 0 5. 9 27.0 35. 5 EE 1. 79 62. 6 6. 0 27. 2 36. 8 E F 1. '72 60. 2 6. 1 27. 7 36. I E G 1. 57. 7 6. 3 28. 2 30. 3

1 Draw pin.

EXAMPLE V Under the conditions set forth in Table V, freshly fringence of 0.005 and a relative viscosity of 38.5 was drawn to a machine draw ratio X of 4.0 in an appaspun nylon yarn of 36.5 relative viscosity was drawn in ratus arrangement of the type shown in FIG. 1.- The 1 1 results obtained under various jet conditions and with difierent jet devices have been reported in the following table in order to illustrate the advantage of having the heated fluid impinge on the yarn in an at least partially 12 the two orifice jet of FIG. 4, at a draw ratio X of 4.0. The yarn was drawn to a denier of about 70 under the conditions and at the speeds indicated in Table VH. KA is a delocalized (no pin, no jet, room temperature) conrestricted zone. IA is a delocalized control run. In JB, 5 trol run. an enclosed two-orifice jet device of the type shown in X-ray examination of the drawn yarn according to the FIG. 4 was used in place of that shown in FIG. 1. For procedures described previously shows that they have runs JC-JF, the jet device was replaced with the arrange-' exceptionally large transverse crystal cross sections, comment of FIG. 6. For run JG, conduits 63 were located bined with a high degree of orientation, as indicated by opposite pins 61 rather than between them. In JC-JG, the low orientation angles. The results are given in temperatures were measured at the orifice of a jet con- Table VIII along with corresponding values for shrinkage duit 63. The yarn Was drawn and wound at a speed of and modulus. Also included, for purposes of comparison, 500 yards/minute. I is a pindrawn control KF prepared from similar yarn Because of the numerous filament breaks at the supspun at 1500 y.p.m., packaged, then drawn 2.90X at a porting pins, runs IF and JG were deemed inoperable. tension of 2.5 .g.p.d. KF has a spun yarn birefringence In JE, drawing tension was reduced to 6 8% of control of 0.020, corresponding to a draw ratio X of 1.56. The .JA. However, yarn shrinkage and retraction percentages total draw ratio is, therefore, 4.5X.

were considerably in excess of those obtained in test run The novel product of this invention, obtained under the JB, i.e., with the enclosed jet device of FIG. 4. In run process conditions of run KD, has a conditioned modulus JD, drawing tension was reduced to 71.5% of control (on the drawing package) of at least 38 g.p.d. and a boil- IA, but shrinkage remained at the relatively high level ofi shrinkage of not over 6.5%. This product is characof 9.0%. terized by a crystallite cross section of at least 1250 A? Table VI Heat Transfer Draw Zone Yarn Properties Run Steam Pres- Steam Temp, Steam Flow, Yarn Temp, Tension, g.p.d. Tension, Per- Shrinkage, Retraction,

sure, p.s.i.g. 0. 0.11m. (3. cent Control Percent Percent a. 15 100. 0 10. 5 2. 1. 2-2 38.7 4. 70 o. 3. 15 100. 0 1o. 6 2. 2. 71.5 9.0 2. 2.15 68.3 8.3 1. 2. 07 65.7 7.5 1. 2. 07 65.7 7.6 1.

1 Control.

7 EXAMPLE v11 Thirty-four filament, 33. 5 relative viscosity poly(hexamethylene adipamide) yarn of 0.005 birefringence was spun at 500 y.p.m. and packaged. The packaged yarn was drawn in the apparatus arrangement of FIG. 1, using 45 of run KE.

Table VII Heat Transfer Draw Zone Windup Run Speed,

y.p.m. Steam Steam Steam Yarn Tension, Tension,

Pressure, Temp., Flow, Temp, g.p.d. Percent p.s.i.g. 0. 0.1.11 1. G. Control 1,000 None 2. 64 100. 0

1 Delocalizcd control.

Table VIII Yarn Properties Crystallite Dimensions Run Orientation angle Mi, Shrinkage, Tenacity, Elongatmn, Width, Breadth, Area, g.p.d. percent g.p.d. percent A., D 11., D010 11.

. IA 10 Average KA 34. 1 10. 7 5. 0 27. 3 34 23 780 15. 7 14. 7 15. 2 KB 37. 5 9. 5 5. 4 28. 2 36 25 900 14. 2 14. 0 14. 1 KC 37. 6 7. 8 5. 5 25. 2 39 25 975 14. 2 13. 6 13. 9 KD 38. 2 6. 5 5. 4 25. 2 43 29 1, 250 12. 4 12. 4 12, 1 KB 38. 2 5. 5 5. 0 30. 3 52 33 1, 720 12.3 12. O 12. 2 K13 33. 5 10.0 37 23 850 15.0 16. 0 15. 5

33 EXAMPLE VIII Pre-packaged 34 filament 66 nylon yarn having a birefringence of 0.005 was drawn (LA) in a FIG. 1 apparatus arrangement, using the jet device of FIG. 4. Draw conditions were as follows: steam pressure p.s.i.g., stream temperature 275 C., machine draw ratio X 4.0, windup speed 500 y.p.m. A control (LB) was prepared from the same pre-packaged yarn under the same draw conditions except that an unheated pin was used. In both runs, modulus was determined on as drawn yarn samples and also after boil-off. Thereafter, fabric samples were prepared from the yarns of runs LA and LB by weaving 104 x 76 count taffeta and scoured in the conventional manner. The crease recovery is determined by means of a modified Monsanto crease recovery test which provides an accurate measurement of fabric The generally accepted method for measuring crease recovery is the Monsanto crease mcovery test which has been described as the Vertical Strip Crease Recovery Test in the American Society for Testing Materials Manual. For the purposes of this example, the test was modified by placing a plate 0.070 inch thick within the fold of the fabric being creased, thus producing a much less sharp crease in the fabric than obtained by the standard method. Recovery from this crease (in two minutes) was determined according to the specified test procedure.

From the tabulated results, it is apparent that the yarn of this invention (LA) not only has a higher initial modulus than conventionally drawn yarn (LB) but also retains a somewhat greater fraction of the initial modulus after boil-oif. The latter improvement correlates well with the improved crease recovery of the scoured fabric.

EXAMPLE IX Ten filament poly(hexamethylene adipamide) yarn of 35.5 relative viscosity was spun and drawn at the maximum operable machine draw ratio and to a denier of 60 in an apparatus arrangement of the type shown in FIG. 3, using the jet device of FIG. 4. As a treating fluid, steam was delivered to the jet at a pressure of 30 p.s.ig. and a temperature of 315 C. The drawn yarn was wound at a speed of 2000 yards/min. Various drawing conditions and yarn properties for test run MA are reported in the following table for purposes of comparison with the corresponding values obtained in run MB in which the jet device was replaced with an unheated draw pin.

From Table X, it is apparent that the process of the invention (run MA) permits drawing at higher draw ratios to obtain yarn of higher tenacity, modulus, crystallinity and denier uniformity, at constant drawing tension, as compared to conventional pin drawing (run MB).

When the test was repeated, using yarn spun from high viscosity vacuum-finished poly(caproamide), similar results were obtained.

EXAMPLE X A polymer mixture consisting of parts polyhexamethyiene adipamide and 20 parts polyhexamethylene isophthalamicle is spun to a 14 filament yarn at yards per minute and immediately drawn (without packaging) at the maximum operable machine draw ratio. For test purposes (run NA), a jet similar to that shown in FIG. 2 is used in the draw zone. This jet, however, has a constricted yarn inlet, slightly larger than the yarn bundle. The outlet, for yarn and steam, is rectangular in cross section. There is a narrow slot parallel with and connected to the yarn passage, permitting easy stringup. The jet is fed with 250 C. superheated steam at 50 p.s.i.g. For comparison, a control N8 is also run at maximum operable draw ratio, using identical yarn and an unheated snubbing pin in the draw zone. Yarn properties are given in the following table.

Table XI Run NA N 8 Draw Ratio, X". (max) 5. 0 5.2 Yarn Tenacity, gpd 7. 8 6. 5 Break Elongation, Percent 15 20 Modulus Mi, gpd 59 50 Shrinkage at 0. dry, percent 11.7 15. 0

The process of this invention is useful in the drawing of most synthetic linear polycarbonamides or nylons, such as those disclosed in US. Pats. Nos. 2,071,250 and 2,071,253. The preparation and spinning of these compounds is described in US. Pats. Nos. 2,130,948, 2,163,- 636 and 2,477,156. Particular examples of such polyamides are those prepared from suitable diamines and dibasic acids, e.g., from hexamethylene diamine and adipic acid and their amide-forming derivatives, and also from terrninai-amino carboxylic acids, e.g., from omega amino caproic acid, omega amino-undecanoic acid and their amide-forming derivatives, such as caprolactarn. Yarns spun from copolyamides, grafted polyarnides, and blends of polyamides with other compatible polymers may also be drawn to good advantage in the process of this invention.

The process is particularly useful in drawing polyamide yarns at high speeds, requiring substantially instantaneous yarn heating. Although marked improvements are obtained at 500 y.p.m., the higher velocity jets disclosed herein, which effectively heat the filaments to the required temperature at exposure times (in the jet enclosure) in the order of from 0.01 to 0.001 second, permit drawing speeds of 2,000 y.p.m. or more, a level unattainable by prior art processes.

The instant process permits very effective single stage drawing, and may be followed by such important operations as setting, relaxing, twisting, crimping, alternate twisting, false twisting, and the like. The instant process is also useful in drawing filaments of modified cross section, e.g., Y, propeller-shaped, trilobal, etc., since substantially no distortion of the desired cross section is involved.

Advantages of the instant invention over prior art procedures include reduced drawing tensions, leading to improved process operability and product mechanical uniformity; elimination of snubbing elements, thereby avoiding frictional problems and the necessity for uniform 15 finish application; and the provision of yarn having reduced shrinkage and retraction values, such yarn being provided in a single step and characterized by both a high retention of initial modulus and improved crystallinity. The drawn yarn can be packaged at reduced tension, owing to its dimensional stability. Furthermore, this yarn can be prepared over a wide range of tenacities at a given elongation. The process can be carried out in a rapid, continuous and economic fashion using either freshly-spun or packaged yarn.

Use of freshly formed or as-spun yarn, prior. to initial packaging, in the practice of this invention is particularly advantageous. Since the as-spun yarn is relatively amorphous, maximum reductions in drawing tension plus added flexibility in drawing and associated operations are facilitated. The necessity of a separate drawing stage or step is eliminated, thereby leading to better mechanical quality due to reduced handling, uniformity of lag time (between spinning and drawing) and elimination of an intervening packaging step. Over-all process.

economy results. However, freshly-formed yarn is substantially amorphous and more stringent control of fluid temperature and pressure during drawing are required in order to insure uniform levels of shrinkage and retraction. When yarn of minimum shrinkage is desired, it has been found that more uniform property levels are obtained when the drawing operation is followed immediately by a coupled, controlled relaxation stage. The additional reductions in shrinkage and retraction are not accompanied by an unacceptable reduction in initial modulus when the process of this invention is employed in the drawing stage.

After drawing with extremely hot air or super-heated steam, it may be desirable to treat the yarn with moisture, preferably prior to packaging, in order to permit the yarn to regain its normal or equilibrium moisture content. Such moisture may be supplied during a subsequent relaxation stage merely by using steam as the relaxing medium. This combined procedure usually leads to further improvements in yarn properties.

The filamentary structures of this invention may contain the usual textile additives such as delusterants, antioxidants and the like. In this respect, the presence of an antioxidant may be desirable when gas at very high temperature is employed. Suitable antioxidants are disclosed in US. Pats. Nos. 2,705,227, 2,640,004, and 2,630,421. Other useful additives are disclosed in US. Pats. Nos. 2,510,777 and 2,345,700. In addition, finish may be applied to the structures, though the uniformity 16 of finish application is not as critical as it is in drawing over or about snubbing elements.

The products of this invention are useful in all conventional textile and industrial applications, especially those which require yarn of improved dimensional stability. Because of their reduced retraction values, the drawn yarn can be packaged on inexpensive disposable shipping cores. The high modulus makes them especially suitable for use in fabrics requiring improved resilience and wrinkle resistance.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A drawn oriented filament consisting essentially of polyhexamethylene adipamide, said filament being characterized by high modulus retention after boil-off, low retraction, a break elongation of at least 25%, an initial modulus of at least 38 grams/denier, a boil-off shrinkage of less than about 6.5% and also by crystalline portions having transverse cross-sectional areas of at least about 1250 square Angstroms and an average orientation angle of lessthan 14, said filament being'at least 35% crystalline.

2. The filament of claim 1 further characterized by a denier variation coefficient of less than 1.5%.

References Cited by the Examiner UNITED STATES PATENTS 2,157,117 5/1939 Miles 260-78 2,289,377 7/1942 Miles 260-78 2,389,655 11/1945 Wende 260-78 2,786,732 3/1957 Gabler 26 078 2,957,225 10/1960 Welch et al. 28-82 2,988,783 6/1961 Miller 61: al. 18-48 3,001,236 9/1961 Maier et 1. "18-48 3,057,040 10/1962 Cuculo 28 82 FOREIGN PATENTS 899,263 6/1962 Great Britain.

OTHER REFERENCES Mark et al.: Physical Chemistry of High Polymeric Systems, Intersciencc, 1950, pp. 357359 and 363. QDZSl PGMSSP.

WILLIAM H. SHORT, Primary Examiner DONALD w. PARKER, Examiner.

A. J. SMEDEROVAC, H. D. ANDERSON,

A ssismnt Examiners. 

1. A DRAWN ORIENTED FILAMENT CONSISTING ESSENTIALLY OF POLYHEXAMETHYLENE ADIPAMIDE, SAID FILAMENT BEING CHARACTERIZED BY HIGH MODULUS RETENTION AFTER BOILL-OFF, LOW RETRACTION, A BREAK ELONGATION OF AT LEAST 25%, AN INITIAL MODULUS OF AT LEAST 38 GRAMS/DENIER, A BOIL-OFF SHRINKAGE OF LESS THAN ABOUT 6.5% AND ALSO BY CRYSTALINE PORTIONS HAVING TRNSVERSE CROSS-SECTIONAL AREAS OF AT LEAST ABOUT 1250 SQUARE ANGSTROMS AND AN AVERAGE ORIENTATION ANGLE OF LESS THAN 14%, SAID FILAMENT BEING AT LEAST 35% CRYSTALLINE. 